The degree of neointimal formation after stent placement in atherosclerotic rabbit iliac arteries is dependent on the underlying plaque

Risk prediction of in-stent restenosis among patients with coronary drug-eluting stents: current clinical approaches and challenges

Introduction: In-stent restenosis (ISR) has been one of the biggest limitations to the success of percutaneous coronary intervention for the treatment of coronary artery disease (CAD). The introduction of drug-eluting stent (DES) was a revolution in the treatment of CAD because these devices drastically reduced ISR to very low levels (<5%). Subsequently, newer generation DES treatments have overcome the drawbacks of first-generation DES, i.e. delayed endothelialization, and late stent thrombosis. However, the issue of late ISR, including neoatherosclerosis after DES implantation especially in high-risk patients and complex lesions, still exists as a challenge to be overcome.Areas covered: We discuss the mechanisms of ISR development including neoatherosclerosis, past and current clinical status of ISR, and methods to predict and overcome this issue from pathological and clinical points of view.Expert opinion: The initial drawbacks of first-generation DES, such as delayed endothelial healing and subsequent risk of late stent thrombosis, have been improved upon by the current generation DES. To achieve better long-term clinical outcomes, further titration of drug-release and polymer degradation profile, strut thickness as well as material innovation are needed.

Nanoengineered Stent Surface to Reduce In-Stent Restenosis in Vivo

In-stent restenosis (ISR) is the leading cause of stent failure and is a direct result of a dysfunctional vascular endothelium and subsequent overgrowth of vascular smooth muscle tissue. TiO₂ nanotubular (NT) arrays have been shown to affect vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs) in vitro by accelerating VEC cell proliferation and migration while suppressing VSMCs. This study investigates for the first time the potentially beneficial effects of TiO₂ NT arrays on vascular tissue in vivo. TiO₂ NT arrays (NT diameter: 90 ± 5 nm, height: 1800 ± 300 nm) were grown on the surface of titanium stents and characterized in terms of surface morphology and stability. Stents were implanted into the iliofemoral artery using an overinflation model (rabbit). After 28 days, stenosis rates were determined. The data show a statistically significant reduction of stenosis by 30% compared to the control. Tissue in the presence of TiO₂ NTs appears more mature, and less neointima is present between struts. In addition, the extra cellular matrix secreted by cells at the interface of the NT arrays shows complete integration into the nanostructured surface. These results document the accelerated restoration of a functional endothelium in the presence of TiO₂ NT arrays and substantiate their beneficial impact on vascular tissue in vivo. Our findings suggest that TiO₂ NT arrays can be used as a drug-free approach for keeping stents patent long-term and have the potential to address ISR.

Review of the TAXUS® Liberté™ SR paclitaxel-eluting coronary stent

The advent of drug-eluting stents has revolutionized the treatment of coronary heart disease. Interventional cardiologists are increasingly treating more complex lesions in patients that would have otherwise required bypass surgery. As a result of technological advances, the second-generation thin strut TAXUS stent--the TAXUS Liberté SR paclitaxel-eluting coronary stent--has now been introduced into routine clinical practice. The Liberté stent has evolved from the currently available TAXUS Express stent to provide enhanced lesion access in challenging anatomies as well as more uniform drug delivery. This article will provide an overview of the TAXUS Liberté stent.

Performance of Self-Expanding Nitinol Stent in a Curved Artery: Impact of Stent Length and Deployment Orientation

The primary aim of this work was to investigate the performance of self-expanding Nitinol stents in a curved artery through finite element analysis. The interaction between a PROTÉGÉTM GPSTM self-expanding Nitinol stent and a stenosed artery, as well as a sheath, was characterized in terms of acute lumen gain, stent underexpansion, incomplete stent apposition, and tissue prolapse. The clinical implications of these parameters were discussed. The impact of stent deployment orientation and the stent length on the arterial wall stress distribution were evaluated. It was found that the maximum principal stress increased by 17.46%, when the deployment orientation of stent was varied at a 5 deg angle. A longer stent led to an increased contact pressure between stent and underlying tissue, which might alleviate the stent migration. However, it also caused a severe hinge effect and arterial stress concentration correspondingly, which might aggravate neointimal hyperplasia. The fundamental understanding of the behavior of a self-expanding stent and its clinical implications will facilitate a better device design.

A novel mouse model of in situ stenting

AIMS

Animal models of stenting are mostly limited to larger animals or involve substantial abdominal surgery in rodents. We aimed to develop a simple, direct model of murine stenting.

METHODS AND RESULTS

We designed a miniature, self-expanding, nitinol wire coil stent that was pre-loaded into a metal stent sheath. This was advanced into the abdominal aorta of the mouse, via femoral access, and the stent deployed. In-stent restenosis was investigated at 1, 3, 7, and 28 days post-stenting. The model was validated by investigation of neointima formation in mice deficient in signalling via the interleukin-1 receptor (IL-1R1), compared with other injury models. Ninety-two per cent of mice undergoing the procedure were successfully stented. All stented vessels were patent. Inflammatory cells were seen in the adventitia and around the stent strut up to 3 days post-stenting. At 3 days, an early neointima was present, building to a mature neointima at 28 days. In mice lacking IL-1R1, the neointima was 64% smaller than that in wild-type controls at the 28-day timepoint, in agreement with other models.

CONCLUSION

This is the first description of a successful model of murine in situ stenting, using a stent specifically tailored for use in small thin-walled arteries. The procedure can be undertaken by a single operator without the need for an advanced level of microsurgical skill and is reliable and reproducible. The utility of this model is demonstrated by a reduction in in-stent restenosis in IL-1R1-deficient mice.

New stent design for use in small coronary arteries during percutaneous coronary intervention

Patients with diabetes mellitus, of female gender, increased age, and/or with peripheral vascular disease often develop coronary stenoses in small caliber vessels. This review describes treatment of these lesions with the paclitaxel-eluting 2.25 mm TAXUS^® Liberté^® Atom™ stent. Given the same stent composition, polymer, antirestenotic drug (paclitaxel), and release kinetics as the first-generation 2.25 mm TAXUS^® Express^® Atom™ stent, the second-generation TAXUS Liberté Atom stent incorporates improved stent design characteristics, including thinner struts (0.0038 versus 0.0052 inches), intended to increase conformability and deliverability. In a porcine noninjured coronary artery model, TAXUS Liberté Atom stent implantation in small vessels demonstrated complete strut tissue coverage compared with the bare metal stent control, suggesting a similar degree of tissue healing between the groups at 30, 90, and 180 days. The prospective, single-armed TAXUS ATLAS Small Vessel trial demonstrated improved instent late loss (0.28 ± 0.45 versus 0.84 ± 0.57 mm, P < 0.001), instent binary restenosis (13.0% versus 38.1%, P < 0.001), and target lesion revascularization (5.8% versus 17.6%, P < 0.001) at nine months with the TAXUS Liberté Atom stent as compared with the bare metal Express stent control, with similar safety measures between the two groups. The TAXUS Liberté Atom also significantly reduced nine-month angiographic rates of both instent late loss (0.28 ± 0.45 versus 0.44 ± 0.61 mm, P = 0.03) and instent binary restenosis (13.0% versus 25.9%, P = 0.02) when compared with the 2.25 mm TAXUS Express Atom control. The observed reduction in target lesion revascularization with the TAXUS Liberté Atom compared with the TAXUS Express Atom at nine months (5.8% versus 13.7%, P = 0.02) was sustained through three years (10.0% versus 22.1%, P = 0.008) with similar, stable safety outcomes between the groups. In conclusion, these data confirm the safety and favorable performance of the TAXUS Liberté Atom stent in the treatment of small coronary vessels.

Preclinical Models of Restenosis and Their Application in the Evaluation of Drug-Eluting Stent Systems

Coronary arterial disease (CAD) is the leading cause of death in the United States, the European Union, and Canada. Percutaneous coronary intervention (PCI) has revolutionized the treatment of CAD, and it is the advent of drug-eluting stent (DES) systems that has effectively allayed much of the challenge of restenosis that has plagued the success of PCI through its 30-year history. However, DES systems have not been a panacea: There yet remain the challenges associated with interventions involving bare metallic stents as well as newly arisen concerns related to the application of DES systems. To effectively address these novel and ongoing issues, animal models are relied on both to project the safety and efficacy of endovascular devices and to provide insight into the pathophysiology underlying the vascular response to injury and mechanisms of restenosis. In this review, preclinical models of restenosis are presented, and their application and limitation in the evaluation of device-based interventional technologies for the treatment of CAD are discussed.

Frequency and consequences of early in-stent lesions after carotid artery stent placement

PURPOSE

To examine the prevalence of in-stent lesions 1 month after carotid artery stent placement with multidetector computed tomography (CT) angiography and to evaluate their possible causes and their consequences during 1-year follow-up.

MATERIALS AND METHODS

Sixty-nine patients with symptomatic carotid artery stenosis underwent multidetector CT angiography of the carotid arteries 1 month after carotid artery stent placement. Patients were followed-up until 1 year after stent placement, when duplex ultrasonography (US) was performed. In-stent lesions were defined as hypo- or hyperattenuating lesions at the stent wall found with multidetector CT. Significant restenosis (70%) at 1 year was defined as a peak systolic velocity of more than 300 cm/sec at duplex US. The Fisher exact test was used to assess the relationship between early in-stent lesions and ischemic events and restenosis.

RESULTS

At 1 month, 14 of the 69 patients (20%) were found to have in-stent lesions. In one patient, the stent was occluded. The other 13 in-stent lesions did not result in significant lumen reduction. In the year following stent placement, no difference in ischemic events was found between patients with (14%) and those without (13%) early in-stent lesions (P = .99). There was no difference in the occurrence of restenosis at 1 year (7% vs 4%, P = .59).

CONCLUSIONS

At 1 month after carotid artery stent placement, in-stent lesions are found in about one-fifth of patients. These lesions do not appear to be related to recurrent ischemic events or to restenosis at 1 year.

Echolucent carotid plaques predict in-stent restenosis after bare metal stenting in native coronary arteries

Echolucent carotid plaque is considered to predict coronary events. This study examined whether echolucent carotid plaque may predict in-stent restenosis (ISR) in coronary arteries. This study included 202 patients who had elective and successful percutaneous coronary intervention (PCI) with bare metal stents in de novo lesions of native coronary arteries for symptomatic coronary artery disease (CAD). Carotid plaque echolucency was assessed by ultrasound with integrated backscatter (IBS) analysis (intima-media IBS value minus adventitia IBS) 1 day before PCI. All patients underwent planned coronary angiography (CAG) at 6 months after PCI, or CAG before 6 months due to acute coronary syndromes. ISR (defined as >50% diameter stenosis) was found in 65 (32%) patients. The calibrated IBS values of carotid plaques were inversely correlated with late luminal loss of the stented lesions. Using multivariate logistic regression analysis, the presence of echolucent carotid plaques (<or=-13.7 dB, arbitrarily determined by an ROC curve) served as an independent predictor of ISR (odds ratio 3.8, 95% CI 1.9-7.3, p=0.01) and target lesion revascularization (n=48) (odds ratio 2.8, 95% CI 1.4-5.7, p=0.01). In conclusion, echolucent carotid plaques with low IBS values were independently and closely associated with ISR in native coronary arteries.

Increased In-Stent Stenosis in ApoE Knockout Mice

OBJECTIVE

We aimed to develop and validate a model of angioplasty and stenting in mice that would allow investigation of the response to stent injury using genetically modified mouse strains.

METHODS AND RESULTS

Aortic segments from either C57BL/6 wild-type or atherosclerotic ApoE-KO mice underwent balloon angioplasty alone or balloon angioplasty and stenting with a 1.25x2.5 mm stainless steel stent. Vessels were carotid-interposition grafted into genetically identical littermate recipients and harvested at 1, 7, 14, or 28 days. In wild-type mice, stenting generated an inflammatory vascular injury response between days 1 to 7, leading to the development of neointimal hyperplasia by day 14, which further increased in area by day 28 leading to the development of in-stent stenosis. Uninjured vessels and vessels injured by balloon angioplasty alone developed minimal neointimal hyperplasia. In stented ApoE-KO mice, neointimal area at 28 days was 30% greater compared with wild-type mice.

CONCLUSIONS

By reproducing important features of human stenting in atherosclerotic mice, we provide the potential to investigate molecular pathways and evaluate novel therapeutic targets for stent injury and restenosis.

Systemic application of anti-ICAM-1 monoclonal antibodies to prevent restenosis in rabbits: an anti-inflammatory strategy

OBJECTIVES

After vascular intervention, cell adhesion molecules such as ICAM-1 and VCAM are fundamental in inflammatory processes. In particular, ICAM-1 expression is strongly associated with macrophage-rich areas in restenotic lesions. Therefore, we hypothesized an anti-restenotic effect by systemic application of anti-ICAM-1 monoclonal antibodies (mAb).

METHODS

Thirty two rabbits underwent balloon angioplasty and stent implantation either in the right or left iliac artery, Animals received either anti-ICAM mAb or saline solution as a control. Animals were sacrificed 7 (n=8) and 14 (n=8) days and tissue was analyzed for basic fibroblast growth factor (bFGF) and transforming growth factor beta (TGF-beta) expression. Sixteen animals were sacrificed 6 months following treatment and tissue was harvested for histomorphometric analysis.

RESULTS

After balloon injury, bFGF significantly increased from 7 to 14 days only in the control group and was significantly higher compared to the anti-ICAM group. At 14 days after stent implantation, controls showed a significant increase of both bFGF and TGF-beta, whereas the anti-ICAM group only showed a significant increase of TGF-beta. Histomorphometric analysis for neointimal growth did not show any differences between control and anti-ICAM groups either after balloon injury or after stent implantation at 6 months.

CONCLUSION

Administration of anti-ICAM-1 mAb following either balloon angioplasty or stent implantation results in a suppression of bFGF in the early phase of restenosis, whereas TGF-beta significantly increases from 7 to 14 days after stent implantation independent of anti-ICAM-1 mAb application. Therefore we conclude that anti-inflammatory strategies are able to interfere with growth factor expression after vascular injury.

Pre-procedural ACE-activity does not predict symptomatic in-stent restenosis

BACKGROUND

Several studies indicate that ACE-activity is related to atherosclerosis. We investigated the correlation between ACE-activity, in plasma as well as in the atherosclerotic plaque, and in-stent restenosis.

METHODS AND RESULTS

ACE-activity was measured in blood samples from 178 patients who underwent a percutaneous coronary intervention with stent placement. During 8 months follow-up, 51 of these patients had an adverse clinical event. ACE-activity did not differ between patients with or without adverse events (21.5 vs. 23.1 nM/ml/min; P=0.36). Tissue samples were obtained with an atherectomy catheter before elective stent placement in another group of 13 patients with de novo stenosis. In this tissue, we determined the ACE-content immunohistologically. These patients were scheduled for follow-up quantitative coronary angiography after 12 months. In this group, the quantity of ACE was not correlated to the late luminal loss (0.31 vs. 0.38 mm; P=0.76).

CONCLUSION

In this study, pre-procedural ACE-activity, in plasma as well as in the atherosclerotic plaque, does not predict the occurrence of in-stent restenosis.

Rat Abdominal Aorta Stenting: A New and Reliable Small Animal Model for In-Stent Restenosis

BACKGROUND

A high throughput animal model may enhance pathophysiological studies to mechanisms of in-stent restenosis (ISR). More and appropriate antibodies and transgenic and knockout strains are available in rats. Consequently, a model for ISR in the rat would be convenient for pathobiological studies. Here we present the full characteristics of a rat ISR model suitable for high throughput stent research.

METHODS

The abdominal aorta of rats was separated from surrounding tissue and a BeStenttrade mark 2 or a Cyphertrade mark sirolimus-eluting stent was locally inserted. After 1, 3, 7, 28 and 56 days, the aortas were harvested, fixed, embedded and cut. Morphometric analysis was performed and inflammation scored.

RESULTS

The neointimal area increased to a maximum after 28 days (0.55 +/- 0.08 mm(2)). Subsequently, the neointimal area slightly decreased. The injury score and the neointimal area were linearly correlated (r = 0.85, p < 0.01). Thrombus formation was present after 1 day. Leukocyte adherence was evident after 1 day, maximal after 3 days (93 +/- 21 cells/section) and decreased thereafter. The inflammation score increased after 3 days to a maximum after 7 days (1.37 +/- 0.06) and declined thereafter. After 28 days the Cypher sirolimus-eluting stent decreased the stenosis in comparison to the BeStent 2 (10.2 +/- 0.85 vs. 18.0 +/- 2.0%, respectively, p < 0.01).

CONCLUSIONS

Stent deployment in the rat abdominal aorta results in thrombus formation, inflammation and neointimal formation. Moreover, there is a linear correlation between the injury score and the neointimal area. These responses resemble ISR events as seen in other animal models. Moreover, a known anti-restenotic stent also reduces neointimal formation in this model. Rat abdominal aorta stenting is a promising animal model for ISR, it is suitable for testing commercially manufactured stents and studying the pathophysiology of ISR.

Effect of plaque debulking before stent implantation on in-stent neointimal proliferation: a serial 3-dimensional intravascular ultrasound study

BACKGROUND

Recent intravascular ultrasound (IVUS) studies have suggested that plaque burden has a role in promoting intimal hyperplasia after stenting. We report on volumetric assessments of in-stent neointimal formation with 3-dimensional IVUS analysis, comparing directional coronary atherectomy (DCA) plus stenting (DCA/stenting) to stenting without DCA.

METHODS

Twenty-four patients (24 lesions) treated with DCA before stenting were matched to 24 patients (24 lesions) receiving stenting without DCA. All stents were a single Multilink stent. In both groups, serial IVUS was performed before and after intervention and during the 6-month follow-up period. The arterial segments that were analyzed with a computer-based contour detection program were the same as the stented segments analyzed on serial studies. These measurements were obtained: (1) lumen volume (LV), (2) stent volume (SV), (3) vessel volume (VV), (4) in-stent neointimal volume (ISV) calculated as SV-LV, and (5) percent in-stent neointimal volume (%ISV) calculated as ([SV-LV]/SV) x 100.

RESULTS

Baseline characteristics of the 2 groups were similar. After intervention, both groups achieved similar LV (140.0 mm(3) DCA/stenting vs 135.2 mm(3) stenting alone). However, the follow-up ISV and %ISV were significantly smaller in the DCA/stenting group (19.6 +/- 12.2 mm(3) DCA/stenting vs 44.6 +/- 29.5 mm(3) stenting alone; P =.00040; 15.3% +/- 10.6% DCA/stenting vs 31.5% +/- 17.7% stenting alone; P =.00040). Consequently, the DCA/stenting group showed a significantly greater follow-up LV (121.0 +/- 51.5 mm(3) DCA/stenting vs 91.5 +/- 26.7 mm(3) stenting alone; P =.016).

CONCLUSIONS

Plaque removal with DCA before stenting inhibits in-stent neointimal hyperplasia.

Early experience with a novel plaque excision system for the treatment of complex coronary lesions

The use of directional coronary atherectomy (DCA) in current practice has been limited. The SilverHawk System is a newly developed plaque excision device that aims to overcome the drawbacks of prior DCA platforms. The device was evaluated in a porcine coronary model and in a series of patients. Procedural variables along with outcomes were reviewed. Quantitative angiography (QCA) was performed and excised tissue fragments were weighed and examined histologically. In porcine cases, pretreatment MLD increased from 0.51 +/- 0.26 to 2.36 +/- 0.59 mm postdebulking and 19.9 +/- 7.6 mg of tissue was retrieved. In human cases, pretreatment MLD increased from 0.8 +/- 0.4 to 2.2 +/- 0.5 mm postdebulking and 15.2 +/- 7.8 mg of tissue was retrieved without complications. These data show that the SilverHawk System may offer significant utility in treating a wide variety of complex coronary lesions.

Debulking and stenting versus debulking only of coronary artery disease in patients treated with cilostazol (final results of ESPRIT)

Stenting inhibits vascular constrictive remodeling after directional coronary atherectomy (DCA). Cilostazol has been reported to control neointimal proliferation after stenting. This study's aim was to examine the effect of debulking and stenting with antirestenotic medication on restenosis. After optimal DCA, 117 lesions were randomly assigned to either the DCA with stent (DCA-stent) (58 lesions) group or the DCA only (59 lesions) group. Multilink stents were implanted in the DCA-stent group. Cilostazol (200 mg/day) without aspirin was administered to both groups for 6 months. Ticlopidine (200 mg/day) was given to the DCA-stent group for 1 month. Serial quantitative angiography and intravascular ultrasound (IVUS) were performed at the time of the procedure and at 6-month follow-up. The primary end point was 6-month angiographic restenosis. Clinical event rates at 1 year were also assessed. Baseline characteristics were similar. All procedures were successful. No adverse effects to cilostazol were observed. Postprocedural lumen diameter was significantly larger (3.27 vs 2.92 mm; p <0.0001) in the DCA-stent group. However, the follow-up lumen diameter was not significantly different (2.53 vs 2.41 mm, DCA-stent vs DCA). IVUS revealed that intimal proliferation was significantly larger in the DCA-stent group (4.2 vs 1.5 mm(2); p <0.0001), which accounted for the similar follow-up lumen area (6.5 vs 7.1 mm(2)). The restenosis rate was low in both groups (5.4% vs 8.9%), and the difference was not significant. Clinical event rates at 1 year were also not significantly different. These results suggest that optimal lesion debulking by DCA does not always need adjunctive stenting if cilostazol is administered.

Arterial remodeling influences the development of intimal hyperplasia after stent implantation

OBJECTIVES

We examined whether preinterventional arterial remodeling influenced the interventional results after stenting.

BACKGROUND

Arterial remodeling is seen in atherosclerotic lesions, and it may play an important role in the early stage of atherosclerosis.

METHODS

We examined 113 lesions that underwent elective stenting using tubular slotted stents under intravascular ultrasound guidance. The lesions were divided into three groups--adequate, intermediate and inadequate remodeling group--according to preinterventional arterial remodeling. The patients were subjected to coronary angiography and intravascular ultrasound evaluation on average 6.4 months after stenting.

RESULTS

At baseline and immediately after stenting, there were no differences in quantitative angiographic analysis among remodeling groups. However, the plaque cross-sectional area (CSA) in the minimal lumen CSA at preintervention and intimal hyperplasia CSA at follow-up were significantly larger in the adequate remodeling group than in the inadequate remodeling group. The restenosis rate of stenting for the lesions with inadequate arterial remodeling was very low (9.4%). A significant positive correlation was found between preinterventional plaque CSA and intimal hyperplasia CSA at follow-up (r = 0.47, p < 0.0001). Moreover, remodeling index significantly correlated with relative intimal hyperplasia CSA (r = 0.28, p < 0.01).

CONCLUSIONS

Preinterventional arterial remodeling influenced the development of intimal hyperplasia after stenting.